- 1Max Planck Institute for Biogeochemistry (MPI), Department for Biogeochemical Processes (BGP), Jena, Germany (hasperen@bgc-jena.mpg.de)
- 2Institute for Environmental Physics (IUP), University of Bremen, Germany
- 3GP-QAT, Universidade do Estado do Amazonas (UEA), Manaus, Brazil
- 4National Institute of Amazonian Research (INPA)
- 5Department of Physics, Universidade de São Paulo (USP)
The Amazon, with its vast wetlands, is a significant hotspot for greenhouse gas emissions. However, the emissions from aquatic systems remain poorly understood. The Rio Negro is one of the main tributaries of the Amazon river but, to date, there have been few measurements on GHG concentrations and fluxes, and none for the upper Rio Negro region.
We present the first continuous measurements of dissolved CO2, CH4, N2O and CO in the Rio Negro, between the cities of Manaus and São Gabriel de Cachoeira (~1000 km). From a moving research vessel, water was sampled continuously from a depth of 50 cm and passed through a bubble-type-equilibrator. A closed air stream was circulated through the equilibrator, and continuously measured by an in-situ FTIR analyzer. In addition, variables such as pH, air and water temperature, DOC and coliform bacteria were determined.
All measured gases were supersaturated in the water with respect to the atmosphere, indicating an outgoing flux toward the atmosphere. CH4 concentrations showed elevated concentrations in the middle Rio Negro, contrasting with CO2, which peaked in the upper and lower Rio Negro. Both CH4 and CO2 displayed distinct hotspot regions, many of which were centered around human settlements and are therefore likely of anthropogenic origin, as also confirmed by the observed bacterial communities. A few hotspots appeared to be linked to surrounding wetlands, which may release large amounts of CH4 during the rising water phase when reconnected to the main river. N2O showed elevated concentrations in the upper Rio Negro, possibly linked to the extensive white sand forest areas in this part of the catchment. CO concentrations showed a clear diurnal pattern, with highest concentrations coinciding with highest incoming solar radiation.
Based on our measurements, we suggest that anthropogenic influences on remote rivers such as the Rio Negro may be greater than previously assumed, potentially affecting the representativeness of both past and future field measurements.
How to cite: van Asperen, H., Warneke, T., Estefani Batista, C., Souza da Silva, J., Rizzo, L., Klemme, A., Lopes e Oliveira, R., Duvoisin Junior, S., Forsberg, B., and Trumbore, S.: Dissolved greenhouse gases in the Rio Negro (Amazonia, Brazil): the influence of humans versus wetlands, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13543, https://doi.org/10.5194/egusphere-egu25-13543, 2025.
